The invention is concerned with a method for determination of the charging state for filtrates of fiber masses used for manufacturing of paper and cardboard.
The amount of harmful substances are followed up at paper and board machines by determination of the charging state of the colloidal filtrates of fiber masses used for manufacturing of paper and cardboard. The reason for the adjusting of the charging states is that the harmful colloidal substances contained in those would be possible to adjust to improve the functioning of the machines. Conventional methods are based on colloidal titration or potentiometric measurements, directly on the filtrated sample. In such a method, an indicator and a cationic reagent is added to the filtrated sample and also to a water amount representing a reference. After that, the equivalent points of the reference and the sample are determined by titration with an anionic agent. The charging state of the sample is calculated on the basis of the consumption of the anionic agent by comparing with the 0-sample (the reference).
The disadvantage with such a method is that it is slow an unpractical and that the colloidal solutions adhere to the measurement equipment.
The object of this method is to develop a quick and precise method, which does not have the disadvantages of the previous methods.
Especially, the object of this invention is to develop a method, with which the measurement of the charging state would be easy to carry out without any troublesome titration.
The method of the invention is mainly characterized in that, the sample is filtrated out from fibers through a filter and indicator color is added to the filtrate in solid state or as a liquid. Thereafter, the absorbance of the filtrate is measured and the charging state of the solution is read from the corresponding place of a previously made calibration curve.
In the construction of the calibration curve, a sufficient amount of samples are taken from the same anionic sample and such different known amounts of cationic agent are added to these samples that at least a part of the samples are cationic and at least a part of the samples are anionic. With the term sufficient amount, it is meant that a sufficient amount of points are achieved to be able to draw a calibration curve. Some kind of a calibration curve can already be drawn with 5-6 samples, but ca 10 samples are needed to achieve an exact curve. The charging states of the filtrated samples are determined in previously known manner, e.g. by cationic titration or by potentiometric measurements. Thereafter, the absorbances corresponding to the charging states of the samples are measured, and a calibration curve is drawn, wherein a given absorbance corresponds to a given charging state. The equivalent point can also be determined mathematically without a drawn curve.
In alternative, the calibration curve can be made so that a sufficient amount of samples are taken from the same anionic sample and such different amounts of cationic agent are added to these samples so that at least a part of the samples are cationic and a part are anionic, after which the same amount of cationic agent is added to all the samples so that all the samples are cationic. The charging states of the filtrated samples are then determined in a previously known way, e.g. by anionic titration, after which the charging states of the samples and the corresponding absorbances are measured. The calibration curve is drawn as above, wherein a given absorbance corresponds to a given charging state.
The absorbance is measured at a wave length, which is within the range of the visual light and at which the indicator absorbs. This most clearly takes place at the wave length of 500 or 615 nm, most preferably the wave length of 615 nm is used. The absorbance is measured with a spectrophotometer.
The indicator is for example p-toluidin or a corresponding indicator that change color when the charging state changes. The amount of the indicator is such that the change of the color during the titration is visible with the bare eye.
The object for the measurement is a filtrate of a mass used as raw material for paper or cardboard, a filtrate of coated reject or some other fiber mass filtrate used in connection with paper manufacturing.
The filtration is performed with a black band filter paper or the like, with which fibers can be filtered out.
The cationic agent is a cationic polymer, polydadmac(trademark) or the like.
The invention is described in more detail in the following in connection with advantageous principle examples and embodiment examples. The invention is not restricted to the details of the examples.
Thus, in the invention, there is made use of the fact that the absorbance of the solution is strongly increased at a certain wave length of light transmitted through the sample, especially at the equivalent point, when a cationic regent is added to the anionic solution, and there is used indicator in the titration, e.g. p-toluidin, added to the solution.
The invention has several advantages compared to the known colloidal titration method. It can especially be mentioned that it is quick and easy to carry out. A practical advantage is that the vessels and tools used, such as cuvettes and mixers etc. stay clean.
The invention can be used as a component of an automatic continuously working measuremtn device of for the measurement of paper processes, also for the cardboard and cellulose industry.
0-sample:
5 ml sample of distilled water or some other practical amount is taken. The 5 ml sample is added to 50 ml of diluted indicator, e.g. a p-toluidin solution. 5 ml of diluted polydadmac solution or some other cationic reagent is added. The equivalent point is determined by titration with diluted potassium polyvinyl sulfate or a corresponding anionic agent, until the color of the solution is permanently changed. The result=A ml.
Titration of the sample:
The sample is titrated in the same way as the zero sample, but instead of distilled water there is used a filtrate of reject or some other fiber mass used in the manufacturing of paper. The filtration takes place through a conventional filter paper used in laboratories.
Calculation of the result:
The result is achieved from the following formula:                     A        ⁢                  xe2x80x83                ⁢        ml            -              B        ⁢                  xe2x80x83                ⁢        ml                    5      ⁢              xe2x80x83            ⁢      ml        ⁢      xe2x80x83    ⁢  meq  ⁢      /    ⁢  ml  ⁢      xe2x80x83    ⁢      (          =              milliequivalents/liter              )  
A and B was determined above and the result is the consumption of anionic agent per sample compared to the consumption of distilled water.
The effect of solid matters can be eliminated before the color addition and by subtracting this result from the final result. Modern apparatuses can do this automatically. Also the effect of the dilution can be eliminated by using more concentrated solutions or by programming the devices to take the dilution into consideration in the calculations.
First, the titration curve is constructed. For example 5 ml of anionic filtrate of a mass used as raw material for paper is taken. The filtration can be carried out with an ordinary black band filter paper or the like. The sample is placed in a cuvette of a calorimeter (spectrophotometer) and 50 ml of diluted p-toluidin indicator color is added during continuous mixing. The absorbance of the solution is measured at a wave length of 615 nm (which is the wave length, at which the indicator absorbs best) of the light going through the sample. Cationic polymer, diluted polydadmac or the like is added. After each addition, it is waited until the titration reaction is ended before the absorption is measured with a calorimeter.
A titration curve is thus obtained, wherein the change of the charging state can be seen as a change in the absorption.
The titration curve can also be constructed with so called xe2x80x9cback titrationxe2x80x9d, i.e. the sample is first made cationic with known amounts of reagent followed by titration as above, but with anionic agent as titration solution. Next, the absorption readings corresponding to given charging states are calibrated on the titration curve.
Ca two dl of the same fiber mass is put in a sufficient amount of decanter glasses. Diluted polydadmac or some other cationic polymer is added until 1% in such a way that the first sample contains a half kilogram of polymer per 1000 kg dry matter, the next contains a kilogram, then one and a half and so on and then it is stirred. The fixing agent, i.e. the cationic polymer, is allowed to effect for 10 min, after which filtration is carried out as above. The intention is that a part of the samples would be anionic and a part of the samples cationic. It does not matter if some sample would be neutral.
The charging state of the five milliliter samples taken from the filtrates is determined with colloidal titration. After that, five milliliters are taken from each sample and mixed with 50 ml diluted indicator color. The absorbances corresponding to the charging states of the samples are measured with a calorimeter and are placed on the titration curve formed above. The relation between the absorbance achieved and the charging state thus obtained can be used in the determination of the charging state of the reject samples without titration, directly colorimetrically.
An own calibration has to be made for each type of mass, as the impurities of the masses might have a negative influence on the results. In other words, it is not possible to read the charging states of the filtrates of groundwood pulp from a calibration curve made for a reject filtrate.
The effects of solid particles on the absorption can be corrected by measuring the absorption of the filtrated samples before the addition of color reagent and by subtracting the error caused by the opacity from the absorbance reading.
The charging state of coated reject is wanted.
A five milliliter sample is taken from the filtrate and is mixed with 50 ml diluted indicator color. The absorbance of the solution is measured at the wave length of 615 nm with a calorimeter and the charging state is read from the corresponding place of the titration curve.
In the following some advantageous examples of the invention are presented. The intention is not to restrict the invention to the details of the examples.